This invention relates to an improved structure of an internally-decelerated starting motor which is equipped with planetary reduction gears.
A prior-art device of the specified type has been as shown in FIG. 1. A.D.C. motor 2 which is a prime mover for the starting motor 1, and which D.C. motor 2 has an end part where an intermediate bracket 3 of reduction gears is fastened in engagement with a yoke 5 of a field assembly 4. A pole 6 is secured to the yoke 5, and for which a permanent magnet member of ferrite is used. An armature 7 has a rotary shaft 8. The front end part of the rotary shaft 8 is journaled in a sleeve bearing 9 which is secured to the inner peripheral surface of the intermediate bracket 3, while the rear end part thereof is journaled in a sleeve bearing 11 which is snugly fitted on the inner peripheral surface of a rear bracket 10 that is fastened in engagement with the rear end part of the yoke 5 of the fields assembly 4. A spur gear 12 is formed at the front end part of the rotary shaft 8, and which drives reduction gear similar to ones to be described later, in engagement therewith. A stopper 13 is installed in a recess 14 formed in the rear end part of the rotary shaft 8, and a retaining ring 15 which is similarly installed. A brush assembly 17 effects the commutation of the armature 7 in sliding contact with a commutator 16, and numeral 18 a thrust washer.
Now the operation of the above construction will be described. The armature 7 is energized through the brush assembly 17 as well as the commutator 16, and receives the energizing force of the permanent magnet from the field assembly 4, to generate a turning force. This turning force is transmitted to the rotary shaft 8, so that the reduction gears similar to ones to be described later (FIG. 2) are driven through the spur gear 12. An output from the reduction gears is transmitted to an internal combustion engine, not shown, and the internal combustion engine is started.
The prior-art device is as stated above. The D.C. motor is not unitarily constructed, but the front end part of the rotary shaft 8 has an open structure, so that the operations of assembling the D.C. motor with the reduction gears are sometimes difficult. In particular, the armature 7 is attracted to the pole 6 constructed of the permanent magnet, in biased fashion, and the eccentricity of the rotary shaft 8 is great, so that the rotatable mounting of the rotary shaft in the sleeve bearing 9 is sometimes difficult. A further disadvantage is that a magnetic member is attracted to the pole 6 through the open end of the D.C. motor. Another disadvantage is that the intermediate bracket 3 is a separate member and increases the number of components. After all, the prior-art device is demeritorious as an electric part for automobiles to be mass-produced.